1. Field of the Invention
The invention generally relates to an image display panel having a transistor array, and an image display apparatus having such an image display panel.
2. Description of the Related Art
Recently, extensive studies have been made on an organic thin film transistor made of an organic semiconductor material, and an organic thin film transistor array having such integrated organic thin film transistors arranged in a matrix. Advantages of the organic thin film transistor and the organic thin film transistor array typically include that they can be made of various materials, fabrication methods and fabrication shapes are highly flexible, they are be easily increased in the size of surface areas, can be made with a simple layer configuration so as to make fabrication processes simple, and can be fabricated using an inexpensive fabrication apparatus. The image display panel having flexibility and the image display apparatus having such an image display panel can be implemented by combining an organic thin film transistor array formed on a film substrate and an image display medium.
In the fabrication of the organic thin film transistor arrays, thin films and circuits can be easily formed by printing, spin coating, and dipping methods. The organic thin film transistor arrays made with these methods can be cheaper than the related art thin film transistors made of a Si semiconductor material. In particular, with an ink-jet printing method, since an ink-jet head is capable of discharging ink droplets directly to plot patterns on a substrate, material usability can be significantly improved. Thus, patterning the inorganic semiconductor layers or electrode materials by ink-jet printing is capable of simplifying the fabrication process, improving the yield rate, and lowering the fabrication cost.
However, at present, there is less reliability in forming wiring patterns in the fabrication of the organic thin film transistor arrays by the ink-jet printing method. Electrochemical migration is a phenomenon where metal is deposited in the form of dendrites between electrodes as a result of voltage being applied between the electrodes under a high-humidity environment. A typical material for forming wiring patterns by ink-jet printing may be nano-metal ink that is made of nano-size metal fine particles dispersed in a solution. The nano-metal ink is mainly formed of inexpensive Ag materials having high conductivity. However, since Ag materials are susceptible to ionmigration (i.e., electrochemical migration; hereinafter also simply called “migration”), it may be necessary to have technology for preventing ionmigration (herein after called “migration preventing technology”) when Ag materials are used in the fabrication of the organic thin film transistor arrays.
As an example of such migration preventing technology, Japanese Patent Application Publication No. 2006-344992 discloses a known technology to prevent moisture intrusion in which an inorganic barrier layer is formed for excluding moisture in the fabrication of the organic thin film transistor arrays. In addition, as another technology that does not rely on the technology to prevent moisture intrusion, a technology is known in which metallic materials such as alloy having excellent electrochemical migration resistance are used in the fabrication of the organic thin film transistor arrays.
Furthermore, it is generally known that organic semiconductor materials utilized for organic thin film transistors are susceptible to electric property degradation with aging when allowed to stand in the air. The electric property degradation with age results from structural changes in the organic semiconductor materials due to oxidization and deterioration with oxygen and moisture in the air. Similar to the above migration preventing technology, Japanese Patent Application Publication No. 2006-156985 discloses a technology in which the electric property degradation in organic semiconductors with aging is also prevented by forming inorganic or organic barrier layers to protect the organic semiconductors in the fabrication of the organic thin film transistor arrays.
However, the application of the above technologies, in which moisture is excluded by forming the barrier layers or metallic materials having excellent electrochemical migration resistance, to the fabrication of the organic thin film transistor arrays results in increasing fabrication cost of the image display panel and the image display apparatus.